Method for plugging a well with a resin

ABSTRACT

This invention relates to a method for carrying out well construction, repair and abandonment operations, which method involves introducing a resin into a well and curing the same to form a seal, plug or connection, wherein the cured resin is expanded to at least the volume occupied by the resin prior to curing (compensating shrinkage), by cooling the well and curing the resin at a reduced temperature and subsequently allowing the well to reach its static bottom hole temperature. This invention also relates to a method for analyzing the setting time, elastic properties, shrinkage/expansion, compressibility or coefficient of thermal expansion of thermosetting resins or oil well cements under simulated reservoir pressure and temperature conditions, which comprises a introducing a sample ( 7 ) of a thermosetting resin or oil well cement into a pressure vessel ( 3 ) that is equipped with a means( 9 ) to provide the pressure and register the volume change; and to the analyzer used by this method.

FIELD OF THE INVENTION

[0001] This invention relates to a method for carrying out wellconstruction, repair and abandonment operations with a thermosettingresin as seal, plug or connection. More in particular, this inventionrelates to a method of improving the gas tightness of sealing materialsin primary cementing, well repair and plugging operations in oil/gaswells.

[0002] This invention also relates to an analyzer for determining thesetting time, elastic properties, shrinkage/expansion, compressibilityand coefficient of thermal expansion of thermosetting resins and oilwell cements under simulated reservoir pressure and temperatureconditions.

BACKGROUND OF THE INVENTION

[0003] The main objectives for drilling an oil or gas well are to createa connection to an oil and/or gas reservoir and to install a conduit(called production tubing) between the reservoir and the surface. Theouter steel protection of a well is called the casing. The casingrequires a gas tight seal between the reservoir and the surface. Toachieve such seal, the annulus (the gap between the casing and therock/formation) is subjected to a cementing (or grouting) operation.This treatment is normally referred to as Primary Cementing. The mainaspects of primary cementing are to isolate flow between differentreservoirs, to withstand the external and internal pressures acting uponthe well by offering structural reinforcement and to prevent corrosionof the steel casing by chemically aggressive reservoir fluids.

[0004] A poor cementing job can result in migration of reservoir fluids,even leading to gas migration through micro-annuli in the well which notonly reduces the cost-effectiveness of the well but may cause a “blowout” resulting in considerable damage. Repair jobs (“secondarycementing”) are possible (in essence forcing more cement into the cracksand micro-annuli). However, they are costly and do not always lead tothe desired results.

[0005] When a well has reached the end of its economical life, the wellneeds to be abandoned in compliance with local regulations. Abandonmentis usually carried out by first plugging each of the casings in a largenumber of sequential steps, cutting and removing these cut steel casingstubs and successively placing large cement plugs in order topermanently seal the well. As only relatively small volumes of cement(typically in the order of 100 m) are used for those plugs, theirquality needs to be excellent as they will have to act as a seal for avery long time.

[0006] One of the major drawbacks of using traditional cementingmaterials such as ‘OPC’ Class G Oil Well Cement (‘OPC’=Ordinary PortlandCement) in plugging operations is that this widely employed materialcannot achieve a gas tight seal due to its inherent shrinkage. The totalchemical contraction can be split between a bulk or external volumeshrinkage (less than 1%), and a matrix internal contraction representing4-6% by volume of the cement slurry, depending upon the cementcomposition (Parcevault, P. A. and Sault, P. H. ‘Cement Shrinkage andElasticity: A new Approach for good zonal Isolation’, paper SPE 13176(1984). The combined shrinkage phenomena cause gas migration throughmicro-annuli and cracks. These are created because of those shrinkagephenomena and the inherently poor adhesion of Oil Well cement to thesteel Casing. The already poor adhesion is even further deteriorated bythe inability to properly clean the surface of the steel casing prior tocementing.

[0007] The use of conventional cementing materials in “remedialsecondary cementing” has the disadvantage that the customary grain sizeis too large to pass freely into the micro-annuli and cracks whichaffect the quality of the seal.

[0008] In the search for effective cementing materials, attention has tobe paid to inter alia the following requirements: the material should begas-tight (i.e. withstand at least 2 bar per m), it should have acontrollable setting time so that a range of temperatures and welldepths (each requiring different conditions) can be coped with, itshould be thermally stable up to 250° C. as well as being chemicallystable against reservoir fluids for a very long period of time and itsrheological properties should be such that pumping through existing oilfield equipment can be carried out without too much problems.

[0009] A wide range of non cementious sealants have been suggested tocope with at least part of the problems outlined herein above. Examplesof such materials are resins (R. Ng and C. H. Phelps: “Phenolic/EpoxyResins for water/Gas Profile Modification and Casing Leak Repair” PaperADSPE #90, presented at the ADIPEC, held in Abu Dhabi (16-19) October1994); phenol-or melamine formaldehyde (W. V. C. de Landro and D.Attong: “Case History: Water Shut-off using Plastic Resin in a High RateGravel pack Well”—Paper SPE 36125 presented at the 4th Latin Americanand Caribbean Petroleum Engineering Conference, held at Port of Spain inTrinidad, Apr. 23-26, 1996); and polyacrylates (U.S. Pat. No. 5,484,020assigned to Shell Oil).

[0010] Although such materials can be instrumental in solving some ofthe problems encountered with traditional, cement-based plugs, there arestill important drawbacks to be reckoned with in terms of handlingaspects, control of setting times and long term durability.

[0011] Also rubbers have been proposed in general for use as pluggingmaterials. Reference is made to U.S. Pat. No. 5,293,938 (assigned toHalliburton Company) directed to the use of compositions consistingessentially of a mixture of a slurry of a hydraulic cement (such asPortland cement) and a vulcanizable rubber latex. Rubbers specificallyreferred to in said U.S. patent specification are natural rubbers,cis-polyisoprene rubber, nitrile-rubber, ethylene-propylene rubber,styrene butadiene rubber, butyl rubber and neoprene rubber.

[0012] The vulcanization of the rubber involves the cross-linking of thepolymer chains which can be accomplished by incorporating one or morecross-linking agents (the most common one being sulphur) in the rubberlatex (latex having been defined as the aqueous dispersion or emulsionof the rubber concerned).

[0013] In European patent No. 325,541 (Merip Tools International S.A)the use of putty (“mastic”) has been disclosed for producing jointsseparating zones in wells. Suitable compounds are formed by liquidelastomers such as fluorosilicones, polysulphides, polythioethers aswell as epoxy or phenolic resins. In addition, from Internationalapplication WO 99/43923 a special class of room temperature vulcanizingsilicone and fluorsilicone rubbers is known that can be advantageouslyemployed in the repair and abandonment of wells.

[0014] Unfortunately, curing of non cementious plugging agents is alsoaccompanied by shrinkage, again potentially leading to micro-annuli andcracks in the sealant and/or lack of bonding of the seal, plug orconnection to its surroundings. This will especially occur if theadhesion of the thermosetting resin to the steel casing surface is lessthan the forces induced by the shrinkage process. It therefore remainsdesirable to further improve existing methods to overcome saiddrawbacks.

SUMMARY OF THE INVENTION

[0015] In accordance with the main embodiment of the invention there isprovided a method for carrying out well construction, repair andabandonment operations, which method involves introducing a resin into awell and curing the same to form a seal, plug or connection, wherein thecured resin is expanded to at least the volume occupied by the resinprior to curing (compensating shrinkage), by cooling the well and curingthe resin at a reduced temperature and subsequently allowing the well toreach its static bottom hole temperature.

[0016] The expression “resin” used in the main claim and throughout thespecification refers to “classic” thermosetting resins, as well asductile, vulcanizable rubbers.

[0017] Another embodiment of the invention comprises a method forremoving a seal, plug or connection made of an expanded resin and usedin well construction, repair and abandonment, comprising the steps of a)cooling the well, until the seal, plug or connection has shrunk loose,and b) removing the loose seal, plug or connection.

[0018] Finally, the invention also provides a method for analyzing thesetting time, elastic properties or shrinkage/expansion of resins orcements used in well construction, repair and abandonment operationsunder simulated reservoir pressure and temperature conditions, and theanalyzer used by that method.

BRIEF DESCRIPTION OF THE DRAWINGS

[0019]FIG. 1 is a schematic representation of a gas migration set-up;and

[0020]FIG. 2 is a schematic representation of a Rubber AugmentationTester (LAB RAT).

DESCRIPTION OF THE INVENTION

[0021] In carrying out the process of the invention a well, preferablyan oil or gas well, is cooled by a significant degree. The degree ofcooling is discussed hereinafter. Next, a—preferablyliquid—thermosetting resin or vulcanizable rubber is introduced andallowed to react (i.e. cure) until a solid, thermoset resin of nearlythe dimensions of the surrounding “mold” is made. When the well is nextallowed to reach its static bottom hole temperature, the seal, plug orconnection will expand more than the well due to the greater thermalexpansion coefficients of resins compared to the base materials of thewell (e.g., carbon steel casing, primary cement having thermalexpansions coefficients in the order of respectively 1.3*10−3 and1.0*10−3 volume % per degree Centigrade (vol %/° C.), whereas that ofresins may be e.g., 50-100× larger). The expansion should at leastcompensate for shrinkage, ensuring gas tightness of the well, and bettereven expand beyond such dimension to ensure a very firm bonding with theplug, seal or connector's environment.

[0022] Using a conventional resin, typically the well should be cooledby up to 100° C., for instance up to 50° C., more suitably from 15 to40° C. For instance, the candidate well may be cooled by circulation or(preferably) by injection of a cold fluid. This can be achieved via aworkstring during a drilling/completion operation, or the completiontubing or coiled tubing for an already completed well. Suitable fluidscan be (sea) water, completion brine, hydrocarbons as e.g. diesel,condensate or (to a lesser extent) a drilling fluid.

[0023] Other methods which could be envisaged is the ‘slurrying’ of ‘DryIce’ (solid Carbon Dioxide) in the injection stream or cooling thisstream at surface with e.g. liquid Nitrogen in a fluid/fluid heatexchanger.

[0024] The degree of cooling depends on various parameters. Forinstance, a practical approach for a well engineer would be to estimatethe degree of cooling on the basis of well properties (e.g. staticbottom hole temperature, length of the well bore, well geometry andpresence of aggressive chemicals), on the basis of the properties of thematerial used in the well (steel, rock, cement), and on the basis of theproperties of the resin (e.g. amount of shrinkage upon curing,difference in thermal expansion coefficient vis-a-vis that of the wellmaterials; rate of curing at the lowered temperature), and on theavailability of a cooling medium. As to the latter parameter; it will beobviously easier for the well engineer to cool a High Pressure/HighTemperature (HPHT) well using ice cold sea water, than to cool a shallowwell in a continental Mediterranean zone, where only lukewarm water isavailable.

[0025] The above cooling temperatures are suggested for resins with noor ordinary shrinkage upon setting and a thermal expansion coefficient20 to 200× that of the well material. Thus, cooling by more than 100° C.will rarely by necessary, unless a resin with exceptionally largeshrinkage and/or exceptionally low thermal expansion coefficient isused.

[0026] Alternatively, and more precisely, the extent of cooling may bedefined by the product of the temperature difference by which the wellis cooled (ΔT in ° C.) and the difference in thermal expansioncoefficient of the resin vis-à-vis that of the well material (ΔX in vol%/° C.). For instance, this product ΔT.ΔX is suitably in the range of0.5 to 10, more suitably in the range of 2.0 to 5, with the range of 3.0to 3.5 being preferred.

[0027] For even more accurate calculations as to the most suitablecooling temperature, without endangering the integrity of the well bytoo excessive expansion, calculations by Finite Element Modeling (FEM),as described by Bosma, Ravi et al may be used (SPE 56536, “DesignApproach to Sealant Selection for the Life of the Well”, presented atthe 1999 SPE Annual Technical Conference and Exhibition, held inHouston, Tex., Oct. 3-6, 1999). In fact, this article describes thedesirability of utilizing expanding ductile sealants, however, withoutany suggestion to cool the well first and use the thermal expansion ofthe thermoset resin to improve its bonding with e.g. the casing. Anothermodel that may be used is described by Theircelin et al (SPE 38598,“Cement design based on Cement Mechanical Response”, SPE Drilling &Completion, December 1998, pp. 266-273).

[0028] To test the accuracy of the determination and/or provide physicaldata on resin behaviour at well conditions, the present invention alsoprovides a specifically designed analyzer. This third embodiment of thepresent invention is described in more detail in the experimentalsection.

[0029] Thermosetting resins have been used in wells (oil, gas, water oreven waste disposal wells) before. Those having a thermal expansioncoefficient significantly greater than 10−3 vol %/° C. may in principlebe used, as long as shrinkage occurring during curing is compensatedfor. Also mixtures of resins as well as mixtures with resins and othermaterials (e.g. Oil Well Cements, whether Ordinary Portland, BlastFurnace Slag or Aluminate) may be used.

[0030] For instance, U.S. Pat. No. 3,170,516 describes the recompletionof wells, particularly oil and gas wells, wherein the bore of a wellpipe is plugged with a liquid mixture of a thermosetting phenoliccondensation resin and a catalytic hardener thereof. Epoxy resincompositions that are curable to hard impermeable solids for use in wellbores have also been described in U.S. Pat. Nos. 3,960,801; 4,921,047;5,314,023; 5,547,027; 5,875,844; 5,875,845; 5,969,006; 6,006,834 and6,012,524; in International application WO 94/21886, and in Europeanpatent application No. 899,417, the contents of which are incorporatedherein by reference. Most of these epoxy resins are base on diglycidylethers of bisphenols, Bisphenol-A and Bisphenol-F in particular, andsuch epoxy resins, if an epoxy resin is used, are preferred.

[0031] Other thermosetting resins that have been used in well boreapplications, incorporated herein by reference, include ureum, phenoland melamine formaldehyde resins (Derwent abstracts 93-124473/15;94-016587/03 and 89-032494/05); latex compositions (U.S. Pat. Nos.3,312,296; 4,537,918; 5,159,980; 5,738,463, and Derwent abstract98-51909/44); the room temperature vulcanizing silicone andfluorsilicone compounds mentioned before; other resins such as disclosedin U.S. Pat. Nos. 4,898,242 and 5,712,314, and novel perfluoroethersilicone hybrids (as disclosed in U.S. Pat. Nos. 5,310,846 and5,342,879) which are marketed by Shin Etsu, Fremont, USA under the tradename SIFEL.

[0032] Suitable thermosetting resins may be selected on the basis of thethermal expansion coefficient of the resulting thermoset resin, and itsreaction (setting) rate. Thus, suitable thermosetting resins are thoseresulting in a thermoset resin preferably having a thermal expansioncoefficient that is greater than 0.0015 vol %/° C., more preferably isin the range of 0.02 to 0.20 vol %/° C. (as measured by the apparatusdisclosed as the third embodiment of this application). Besides, thethermoset resin should set sufficiently quickly to benefit from thethermal expansion coefficient when the well temperature increases, e.g.it should react fully in the order of hours compared with the tens ofhours required to allow the well to regain its initial (bottom holestatic) temperature. Furthermore, suitable resins should be imperviousto gas, oil, brines and well-treating chemicals at well operatingtemperatures and pressures.

[0033] Particularly suitable resins for use in the methods of thepresent invention are elastomeric thermoset resins. For instance, thevulcanizable rubbers of U.S. Pat. No. 5,293,938; European patentapplication No. 325,541 and/or international application WO 99/43923,all incorporated by reference, may be used.

[0034] With respect to the thermosetting resins mentioned before and inthe section on the background of the invention those of WO 99/43923 areparticularly preferred. These RTV silicone rubbers include thecondensation products of silanol terminated polymers with across-linking agent, as well as the addition/curing (fluor)siliconecompositions described therein.

[0035] Good results in accordance with the present invention can beobtained when using a two component Room Temperature Vulcanizing (RTV)silicone rubber or fluor-containing RTV silicone rubber. Such twocomponent systems comprise two base chemicals: a hydride functionalsilicone cross linking agent and a vinyl functional silicone polymer.When these base compounds are brought into contact they will react,presumably via the addition-curing principle as discussed herein before,thereby producing a (fluor)silicone rubber or gel type material. One ofthe advantages of this curing system is that it does not require anexternal reagent to initiate reaction (like water, e.g. present in moistair). A further advantage of this curing system is that it does notproduce unwanted or damaging by products like alcohols or acetic acid.It is also not limited by diffusion of one of the reactants (e.g. moistair) into the other very viscous component. Therefore, the reaction ofthe two components will proceed independently of their respectivevolumes.

[0036] International application No. WO 99/43923 describes RTV(fluor)silicone rubbers for: (1) zonal isolation, a) as an alternativeto primary cementing in conventional well completion applications, or b)in combination with Expandable Tubing (cf. PCT/EP00/03039); (2) as wellrepair method for corroded tubing, and (3) to fill External CasingPackers. It should be realized that the method of the present inventioncan be used in a similar fashion.

[0037] As such, the thermosetting agent is placed in the well, at adesired depth and location (e.g. in the annulus during a primarycementation or as a plug, in a “plug and abandonment” operation). Priorto placement, the well will have been cooled by one of the methodsdescribed in the preceding text.

[0038] Due to the (significantly) higher thermal expansion of thethermoset resin (e.g., the RTV (fluor)silicone rubbers described in WO99/43923 expand by some 0.06-0.08 vol %/° C.), the resin will expandmore than the rest of the completion upon re-heating of the well,which 1) will more than compensate for any shrinkage incurred during thesetting of the resin (typically some 0.6% upon setting from the liquidto the solid phase) and 2) will improve the chemical and/or physicaladhesion process of the resin to the casing wall.

[0039] The seal may be further improved by enclosing it between a cementpre-flush and after-flush. To enable the placement of such acement-resin-cement sandwich in a Plug and Abandonment (P & A)application, the cement pre-flush preferably has a higher density thanthe thermosetting resin which may be achieved by the addition ofconventional weighting agents such as barite, hematite, trimagnesiumtetroxide, and the like.

[0040] Similarly, the cement after-flush preferably has a lower densitythan the thermosetting resin, e.g. by the addition of extenders e.g.lightweight fillers, hollow microbeads and the like.

[0041] According to another embodiment, which is basically an extensionof the embodiment described herein before, the invention also provides amethod for removing a seal made of a thermoset, expanded resin, bycooling the well wherein the seal is used until the seal hassufficiently shrunk to allow its (non-destructive) removal.

[0042] Whilst the above process has been described in combination withwell technology applications, it should be realized that the inventionis not so limited. Indeed, the process of the present invention may alsobe applied in surface facilities (e.g. temporary or permanent pluggingof pipelines and/or risers during e.g. platform (de)commissioningactivities, and abandonment of pipelines and the like).

[0043] The specific formulations can for instance be tested in thelarge-scale gas migration rig which has been described by Bosma et al in“Cementing: How to achieve Zonal Isolation” as presented at the 1997Offshore Mediterranean Conference, held in Ravenna, Italy andincorporated herein for reference). The equipment comprises in essence a4 meter high, 17.8×12.7 cm (7×5 inch) steel annular casing lay-out plusa 50 cm high simulated permeable (3000 mD) reservoir. The equipment canbe operated at pressures up to 6 barg and 80° C. The breakthrough of gasin the evaluation of the dynamic gas sealing ability of a candidatesealing agent (e.g. cement or another material) during setting ismonitored by flow transducers and, in addition, pressure and temperaturetransducers placed equidistantly across the height of the column. Atypical experiment is performed by applying and maintaining awell-defined overbalance between cement column and “reservoir” pressureand monitoring the dependent parameters (flow, pressures andtemperatures) versus time.

[0044] It is also possible to use a static type of test equipment, e.g.as described in the paper SPE 1376 presented by P. A. Parceveaux and P.H. Sault at the 59th Annual Technical Conference and Exhibition inHouston, Texas (Sep. 16-19, 1984) entitled “Cement Shrinkage andElasticity: A New Approach for a Good Zonal Isolation”. The testequipment is in essence a high pressure static gas migration apparatuswhich can be operated up to 200 barg and 150° C. and comprises acylinder in which appropriate internals such as plugs or annular casingconfigurations can be simulated. Typically a cement (or other material)is allowed to set inside the cylinder at static conditions (i.e. nodelta P). The sealant is either present as single phase of a resin, ahybrid (e.g. a mixture of rubber latex compositions or RTV (fluor)silicone rubbers with Oil Well Cements, either Ordinary Portland Cement,Blast Furnace Slag, or Aluminate) or a sandwich of a thermoset rubberwith a conventional Oil Well Cement (either Ordinary Portland Cement,Blast Furnace Slag, or Aluminate) on top of it (seen in the direction ofthe gas flow. The resins are placed in this cell at a certaintemperature (typically reflecting that of the cooled down well) anddownhole pressure and allowed to set, whilst concurrently the cell isheated further to the final Bottom Hole Static Temperature (BHST) of thewell (time frame approximately one half to one day). Subsequently, thepossible onset of gas leakage is monitored by applying increasingpressure differentials across the plug or annular casing configuration,by decreasing the back pressure at the top of the plug. To calibrate thetest equipment default cement formulations can be used.

[0045] The present invention also provides a method of analyzing thesetting time, elastic properties, shrinkage/expansion, compressibilityor coefficient of thermal expansion of thermosetting resins or oil wellcements under simulated reservoir pressure and temperature conditions,which comprises:

[0046] introducing a sample of a thermosetting resin or oil well cementinto a pressure vessel that is equipped with a means to provide thepressure and register the volume change, and that can accurately mimicrealistic oil field conditions;

[0047] at least partly immersing a body in the sample;

[0048] filling the remaining volume of the vessel;

[0049] exciting the body by an external outside force; and

[0050] monitoring the progress of the setting reaction on a continuousbasis by a frequency (vibration) measurement, which encompasses thedetermination of the changing Resonance Frequency of the body that is atleast partly immersed in the sample and which is excited by an externaloutside force.

[0051] The vessel may, for instance, be filled with a fluid that iseither hydrophilic or hydrophobic, depending on the nature of the sampleto be investigated.

[0052] The means to provide the pressure and to register the volumechange may be a pump or the like. For instance, excellent results havebeen obtained using a syringe pump that is capable of maintainingconstant pressure by moving a piston.

[0053] The body may be a flat spring, that is moving in the lateraldirection. Alternatively, it may be a small cylinder, plate or the likemoving in the axial direction.

[0054] The body is preferably moved by an external magnetic field, butit may also be operated mechanically or similar fashion.

[0055] The present invention also provides an analyzer for determiningthe setting time, elastic properties, shrinkage/expansion,compressibility or coefficient of thermal expansion of thermosettingresins or oil well cements by the methods described above.

[0056] Preferably, the analyzer is equipped with a flat spring that isexcited by an external magnetic field, a syringe pump, and a nonmagnetic pressure vessel. The most preferred analyzer is described inthe experimental section.

[0057] The invention will now be illustrated by the following, nonlimiting Examples.

[0058] Test Equipment, the Large-Scale Migration Set-Up of FIG. 1

[0059] In FIG. 1 is shown a test set-up including a cylindrical pressurevessel 1 provided with opposite end plates 2, 3, and an electricalheater 4 is arranged around the vessel 1.

[0060] A plug composed of a thermosetting resin part 6 and a cement part8, is arranged in the pressure vessel 1. A filter layer 10 is arrangedin the pressure vessel 1, between the first resin part 6 and the lowerend plate 3. A temperature sensor T is arranged in the pressure vessel1, between the cement part 8 and the end plate 2. A gas container Gc isin fluid communication with the interior of the pressure vessel 1 at thelower end thereof via a hydraulic line 10, and a back pressurecontroller Bpc is in fluid communication with the interior of thepressure vessel 1 at the upper end thereof via a hydraulic line 12.Hydraulic line 12 is provided with a flow indicator F, and pressuregauges P are provided at the respective hydraulic lines 10, 12. Acontrollable valve 14 is provided in a third hydraulic line 16interconnecting hydraulic lines 10, 12. The test set-up had a diameterof 14 cm and a length of 115 cm.

EXAMPLE 1

[0061] A series of experiments were conducted with the large-scalemigration set-up as described above. As thermosetting resin an RTVsilicon rubber (based on DC 3-4230 from the Dow Corning Corporation,Midland, USA, and formulated to have a density of 2.33 g/cc, usingsilica flour and Microfine Steel (100 Micron e.g. A-100 S ex Höganäs AB,Höganäs, Sweden) was selected, having a setting time of 6 hours at 100°C. A cement with a density of 1.92 g/cc and a setting time of 5 hours at100° C. was placed on top of the resin. The simulated seal measuredabout 0.5 m of resin and 0.5 m of cement.

[0062] The vessel 1 was closed and pressurized up to 200 barg by meansof the gas pressure provided by the gas container GC. Whilst the resinand cement were setting, the set-up was heated within a time frame ofhalf a day from 100° C. to 130° C., the simulated BHST of the well, toinduce expansion of the resin. Next, the pressure drop across the plugwas increased in steps of about 10 bar up to 200 bar by successivelydecreasing the back pressure at the top of the plug by means of the backpressure controller BPC in order to determine the sealing capacity ofthe plug. The resin/cement sandwich appeared to be fully gas tight up to200 bar differential pressure, which was the limit of the test.

[0063] The experiment was repeated with the set-up in a slantedposition, simulating a well with a 50° inclination vis-à-vis a verticalwell. Again the seal withstood successfully the full 200 bar pressuredifferential.

COMPARATIVE EXAMPLE 1

[0064] The aforementioned experiments were repeated, however, with acuring temperature of 130° C. instead of 100° C. and using a similarsandwich consisting of RTV Silicone Rubber and Class G Oil Well cement.This comparative experiment simulates the abandoning of an oil/gas wellwithout pre-cooling. The sealing capacity of the plug was only 30 bar,using a vertical set-up.

[0065] The experimental results show the gas tightness obtained whenpre-cooling a simulated oil/gas well by using a standard cement and anaddition-curing silicone formulation, in particular when applying suchformulations in sandwich type plugs.

[0066] Test Equipment, Analyzer at Down Hole T and P Conditions

[0067] To determine the setting behaviour, elastic/viscosity propertiesand volume changes of the sealant materials (resin and cement) ananalyzer was developed as hereinafter described. A schematicrepresentation of the analyzer is shown in FIG. 2.

[0068] This analyzer comprises a pressure vessel 20 to hold the sample22, and a syringe pump 24 to provide the pressure and register thevolume change.

[0069] Pressure vessel 20 is a non magnetic (e.g. INCONEL) (INCONEL is atrademark) High Pressure, High Temperature Pressure vessel, which canaccurately mimic realistic oil field conditions.

[0070] The remaining volume of the vessel is occupied by a‘pressurization liquid’ that may be either hydrophilic or hydrophobic,depending on the nature of the reacting system to be investigated.

[0071] Pump 24 is capable of maintaining constant pressure by moving apiston 26.

[0072] The progress of the setting reaction is monitored on a continuousbasis by a frequency (vibration) measurement. It encompasses thedetermination of the changing Resonance Frequency of a flat spring 28which is excited by an external Magnetic Field generated by a drivingcoil 30 (the frequency being continuously swept over a frequency rangeof some 10-70 Hz). The spring is partly immersed by the resin/cementsystem to be tested and as such its resonance frequency will increase asthe medium (in which it is immersed) will gradually ‘harden’.

[0073] The system can be either volume or pressure controlled,reflecting an isobaric or isochoric operational mode.

[0074] In a typical experiment, a continuous frequency sweep (rangingfrom 10 Hz to 70 Hz) is applied by means of the driving coil 30 onto theflat spring 28 which is fixed at the vessel bottom at one end and whichis fully free at the other end. A tiny permanent magnet 32 is mounted atthe spring 28 by a magnet holder 33 for excitation of the spring, dueits interaction with the continuously changing external magnetic fieldof the driving coil 30.

[0075] The input magnetic energy, which will result into an oscillationof the spring is fed into the pressure vessel by a highly magneticallyconductive pole shoe (not shown). The changing resonance frequencyresponse of the spring due to the change of the viscosity of thethermosetting resin or the oil well cement, is detected by a secondelectromagnetic coil 34 (externally mounted on a second pole shoe). Theoutput signal is then electronically conditioned prior to furtherprocessing.

[0076] The amplitude of the spring and its continuous change ofresonance frequency is fully automatically recorded by a DataAcquisition system (hosted by a portable PC).

[0077] The damping characteristics of the spring system (being relatedto the viscosity of the resin/cement and the ‘Spring Constant’ (beingrelated to the elasticity of the liquid or solid) can be determined byan internal algorithm.

[0078] As such not only a very clear monitoring of the onset ofgelling/setting of oil well cements (and a multitude of resins and selfvulcanizing rubbers) can be determined at in-situ well conditions, butalso more fundamental data (elasticity modulus, viscosity), which can beused for well engineering design.

[0079] The analyzer may also be used to determine the volume changes (atisobaric conditions) or alternatively the pressure changes (at isochoricconditions), whilst allowing the candidate cement or resin to set. Bothmeasurements can be performed at either isothermal conditions or forprescribed temperature sweeps over time.

[0080] In this manner, the volumetric properties (shrinkage orexpansion) of resins or oil well cements can be determined, oralternatively their compressibility behaviour (in a time range from theonset of gelling up to far beyond ‘final set’ of the resin/cement) canbe measured.

[0081] Also, the apparatus is capable to determine the volume change ofthe materials under investigation as a function of temperature (i.e. thevolumetric thermal expansion coefficient, at isobaric conditions), bysweeping the temperature inside the vessel over a certain time period(max delta T of the prototype is about 270° C., i.e. −20° C. to +250°C.), whilst maintaining the applied pressure. (The maximum operatingpressure of the prototype is 1500 barg).

[0082] The latter (volume change) features can be de-coupled from thefrequency exciter set up (i.e. determination of theresonance-frequency), described earlier, and constructed as a separateapparatus.

EXAMPLE 2

[0083] The analyzer was used to measure the thermal expansioncoefficient of the aforementioned RTV Silicone rubber, DC 3-4230 (ex DowCorning, Midland, USA), being about 0.066 vol % per ° C. (at 200 barg),and to measure the volume change of the resin during setting (at 100°C., and 200 barg), being about −0.5 vol %.

[0084] By comparison, a conventional Class G Oil Well Cement with aWater to cement ratio of 0.40, showed a total shrinkage of some 4-5% (at100° C., and 200 barg), after final setting and a thermal expansioncoefficient of 0.001 vol % per ° C. (at 200 barg).

1. A method for carrying out well construction, repair and abandonmentoperations, which method involves introducing a resin into a well andcuring the same to form a seal, plug or connection, wherein the curedresin is expanded to at least the volume occupied by the resin prior tocuring (compensating shrinkage), by cooling the well and curing theresin at a reduced temperature and subsequently allowing the well toreach its static bottom hole temperature.
 2. The method of claim 1,wherein the well is cooled by up to 100° C., preferably up to 50° C.,more preferably from 15 to 40° C.
 3. The method of claim 1, wherein theextent of cooling is defined by the product of the temperaturedifference by which the well is cooled (ΔT in ° C.) and the differencein thermal expansion coefficient of the resin vis-à-vis that of the wellmaterial (ΔX in vol %/° C.), and wherein this product ΔT.ΔX is in therange of 0.5 to 10, preferably in the range of 2.0 to 5.0, with therange of 3.0 to 3.5 being most preferred.
 4. The method of any one ofclaims 1 to 3, wherein the well is cooled by circulation or injection ofa cold fluid.
 5. The method of claim 4, wherein the well is cooled via aworkstring during a drilling/completion operation, or via the completiontubing or coiled tubing for an already completed well.
 6. The method ofclaim 4, wherein the well is cooled with (sea) water, completion brine,hydrocarbons as e.g. diesel, condensate or a drilling fluid, or byslurrying of dry ice in the injection stream or cooling this stream atthe surface with liquid nitrogen in a fluid/fluid heat exchanger.
 7. Themethod of any one of claims 1 to 6, wherein a resin is used selectedfrom one or more of: phenolic condensation resins; epoxy resincompositions, in particular based on diglycidyl ethers of bisphenols;ureum, phenol and melamine formaldehyde resins; latex compositions; roomtemperature vulcanizing silicone and fluorsilicone compounds andperfluoroether silicone hybrids.
 8. The method of any one of claims 1 to7, wherein the resin has a thermal expansion coefficient that is greaterthan 0.001 vol %/° C., more preferably is in the range of 0.02 to 0.2vol %/° C. (measured by the apparatus described in claim 14).
 9. Themethod of any one of claims 1 to 8, wherein the resin is a vulcanizablerubber, selected from natural rubbers, cis-polyisoprene rubber,nitrile-rubber, ethylene-propylene rubber, styrene butadiene rubber,butyl rubber, neoprene rubber, silicone rubbers, preferably an RTVsilicone rubber and/or a fluor-containing RTV silicone rubber.
 10. Themethods of any claims 1 to 9 where a hybrid of the rubbers mentioned inclaim 9 plus conventional Oil Well Cement (whether Ordinary PortlandCement, Blast Furnace Slag or Aluminate) is used.
 11. The method of anyone of claims 1 to 10, wherein a cement pre-flush and/or after-flush isused.
 12. The method of claim 11, where, in a Plug and AbandonmentOperation, the cement pre-flush, if any, has a higher density than theresin, and/or wherein the cement after-flush, if any, has a lowerdensity than the resin.
 13. A method for removing a seal, plug orconnection made of an expanded resin as described in any one of claims 1to 12, by cooling the well wherein the seal, plug or connection is useduntil the seal, plug or connection has shrunk loose, and removing theloose seal, plug or connection.
 14. A method of analyzing the settingtime, elastic properties, shrinkage/expansion, compressibility orcoefficient of thermal expansion of thermosetting resins or oil wellcements under simulated reservoir pressure and temperature conditions,which comprises: introducing a sample (7) of a thermosetting resin oroil well cement into a pressure vessel (3) that is equipped with a means(9) to provide the pressure and register the volume change and that canaccurately mimic realistic oil field conditions; at least partlyimmersing a body in the sample (7); filling the remaining volume of thevessel; exciting the body by an external outside force; and monitoringthe progress of the setting reaction on a continuous basis by afrequency (vibration) measurement, which encompasses the determinationof the changing Resonance Frequency of the body that is at least partlyimmersed in the sample and which is excited by the external outsideforce.
 15. The method of claim 14, wherein the sample (7) is introducedinto a non magnetic High Pressure, High Temperature Pressure vessel (3),that is equipped with a pump (9) capable of maintaining constantpressure by moving a piston; the body that is at least partly immersedis a flat spring; and wherein the external outside force that is used toexcite the body is an external Magnetic Field.
 16. An analyzer foranalyzing the setting time, elastic properties, shrinkage/expansion,compressibility or coefficient of thermal expansion of thermosettingresins or oil well cements under simulated reservoir pressure andtemperature conditions by the method as claimed in claims 14 or 15.